1. Field of the Invention
The present invention relates to a process for preparing polyethylene. The present invention particularly relates to preparing high density polyethylene using a slurry loop reactor.
2. Background of the Art
It is well known in the art of manufacturing chemicals in general and polymers in particular to use a reactor consisting of a pipe containing a flowing stream of reactants. One such pipe reactor is known as the slurry loop reactor. In a slurry loop reactor, reactants are feed into a pipe containing a solvent and a catalyst. The admixture of solvent, reactants, and catalyst are continuously recycled through the pipe, hence the term “loop,” with the reaction product being continuously removed.
In the manufacture of high density polyethylene, particles of polyethylene can be removed from the reactor by means of a settling leg. U.S. Pat. No. 3,293,000 to Marwil discloses the use of settling legs in a loop reactor for manufacturing an ethylene butane copolymer. In this reference, the settling leg functions to allow a portion of the polymer slurry to escape from the loop into outlets that allow the particles to be gravimetrically removed.
While technology for preparing polymers has changed with respect to catalysts and reactants, the same general loop reactor technology employed in the 1960s is still in use. For example, U.S. Pat. No. 4,613,484 to Ayres, et al., discloses an improvement to settling legs, also referred to as accumulator legs, is disclosed. This technology is still generally current and in present use, particularly for the production high density polyethylene.
Despite loop reactors having been used for a long time, the process of starting a running a loop reactor is not without problems. U.S. Pat. No. 6,303,825 to Gerlich, et al. discloses a method of starting up a loop reactor system. This reference suggests using a microprocessor to automate starting up and running a loop reactor. One suggested algorithm recognizes the end of the startup of the reactor and then controls the reactor at steady state.